Method and apparatus for the transfer of loads from a floating vessel to another or to a fixed installation

ABSTRACT

A method and apparatus for the transfer of loads from a vessel that moves with heavy seas to a stationary or mobile installation by the use of at least one lifting cable and at least one hoisting mechanism, where the load, in a starting position, stands on a rack on the vessel. The load transfer takes place at an instant when the load has only insignificant kinetic energy, as the gripping mechanism is activated in a controlled manner at the instant to lock the load to the lifting cable. At the same instant the rack collapses and immediately establishes a distance between the load and the vessel, thereby suspending the load on the lifting cable.

The invention relates to a method for transfer of loads from a vesselthat moves with heavy seas to a stationary or mobile installation, bythe use of at least one lifting cable or wire and at least one hoistingmeans, where the load in its starting position stands on a rack on thevessel.

The invention also relates to an apparatus for transferring a loadmovable in a substantially vertical direction to a temporarilystationary suspending means such as a cable or string at an instant whenthe load has no significant kinetic energy.

The invention relates also to a method for constructing an oil platformon a Jacket or support structure positioned on the sea bed, preferablywith the aid of the method and apparatus mentioned above.

In connection with Norwegian patent no. 159 186 and with patentapplication NO 894 762, further developmental work has been carried outwith the objective of devising a method for direct installation ofmodules from a ship to a platform in accordance with the constructionmethod previously described in the above cited patent publication. Therehas also been developed a type of platform consisting of a system ofeasily mountable and dismountable modules, deck and equipment which mayeasily be mounted directly from barges or a supply ship on the fieldwithout using floating cranes.

The methods currently in use today for offshore load transfer, bylifting loads from a ship to fixed or mobile installations, involvesubjecting the lifting gear as well as the loads to some verysignificant dynamic stresses in that the loads are transferred whilstthey are in motion, and consequently have high kinetic energy.

In the transfer of smaller loads, for example service goods and supportequipment for production platforms and drilling rigs, the dynamic forcesare absorbed by existing cranes and lifting gear with the aid ofhydraulic cylinders and hydraulic accumulators, so-called heavecompensators. Also, the cranes currently used on board oil platforms arelimited to weights of 15-80 tons.

In lifting of heavier equipment, such as modules, foundation frames,manifold stations, etc., having weights from 100 to 7000 tons, thedynamic forces will be so considerable that lifting with cranes placedon the platforms is not practically feasible. Such weights are currentlyonly lifted with floating cranes of various types. Most of these cranesare also equipped with hydraulic compensator systems to dampen theeffect of the dynamic loads.

A major disadvantage with the use of contemporary lifting equipment isit physical size and the fact that the lifting and load handling musttake place over other equipment. This entails particular limitationswith respect to access, for example, in installation of equipment ormodules situated under the platform.

Furthermore, the lifting of heavier units over the vital parts of theplatform, such as processing plants, etc., means that processing must bestopped for security reasons during the period in which lifting takesplace. The financial consequences of this can be very considerable.

In addition, the huge floating cranes must be mobilized and anchored atthe platform. This involves special complications when the sea bedaround the platforms is overlaid with pipeline systems, manifolds, etc.,which can be damaged by anchors and chains. Furthermore, the cranevessel will normally require the assistance of 2-4 tugboats or supplyships for the anchoring, etc. Barges are needed to bring out modules andheavier equipment--usually one standard barge with a 10,000 tondisplacement, pulled by two tugboats or supply ships.

The mobilization time and mobilization costs, in addition to operatingcosts for this equipment, are quite significant, even though the liftingoperation itself takes only a short time.

Therefore, current methods establish clear limitations, both technicallyand financially, for direct lifting operations onto platforms ordrilling rigs.

The limitations mentioned above are overcome by the present invention,which permits load transfer directly from a ship or barge to a platform,from ship to ship or from ship to drilling rig without any significantinfluences of dynamic loads. The equipment of which the inventionconsists is lightweight, and may be positioned on or under the platformby means of simple auxiliary units.

With the aid of the invention a special platform type and method ofconstruction has been developed, namely a platform with dependingmodules that fulfills all requirements for simple, inexpensive andflexible assembly, replacement of modules and later dismounting.

There are no known limitations as to the weights that can be handled inaccordance with the method.

The method is particularly designed for load transfer in connection withrebuilding and or construction of oil platforms, and the transfer ofloads such as foundation frames, satellite stations, modules, etc.

The present method utilizes a principle based on carrying out a loadtransfer at the moment in time when the load does not have anysignificant kinetic energy.

The energy of the load, as is commonly known, is proportional to thesquare of the velocity at the moment of load pick-up, expressed by theformula:

    W=1/2*m*V.sup.2

The vertical speed of the object to be lifted is a function of theship's movements, and given the fact that the ship follows the motion ofthe wave, the velocity for regular waves is a sine function with aperiod of about 4 to 8 seconds in the transfer situations that have beencalculated.

The theoretical method for load transfer should thus be to seize theload at the instant it is at the top or the bottom of the wave and istherefore without any vertical velocity component.

In purely practical terms, it is only conceivable to do this while theload is on the top of the wave, due to the risk of collision between theship and the load if the lifting speed is slower than the ship'svertical velocity in the wave.

For this purpose, a method and apparatus have been developed to ensurethat the load is transferred in the described manner.

In accordance with the present invention, there is provided a method ofthe type described in the introduction, which is characterized in thatthe load transfer takes place at an instant when the load has onlyinsignificant kinetic energy, as at least one gripping means isactivated in controlled manner at said instant to lock the load to thelifting cable, and at the same instant, the rack collapses andimmediately establishes a distance between the load and the vessel,thereby suspending the load in the lifting cable.

In accordance with the invention there is also provided an apparatus ofthe type mentioned in the introduction which is characterized in that Itcomprises at least one gripping means and a sensor device that registerswhen the movement of the load reverses at said instant, which sensordevice emits a signal that controllably activates the gripping means tolock the load to the suspending means at the same instant.

In accordance with the present invention there is also provided a methodfor the construction of an oil platform as mentioned in theintroduction, which is characterized in that the platform is constructedby the hoisting of large building modules directly from a mobile vesselup from below through the main frame system of the platform forinstallation between the main frame system or on the top thereof.

Additional features of the Invention are disclosed in the dependentclaims.

Other additional objectives, features and advantages will be apparentfrom the following description of the invention, which is provided forthe purpose of description without thereby limiting the invention, andare presented in connection with the attached drawings, where:

FIG. 1 shows an apparatus according to the invention which is a part ofthe equipment used to carry out a load transfer,

FIG. 2 is a diagram illustrating the placement of a plurality ofapparatuses according to the invention to execute a load transfer from avessel to a stationary installation,

FIG. 3 shows the apparatus according to FIG. 1 in further detail andpartial section,

FIG. 4 is an enlargement of an alternative embodiment of the apparatusshown in FIG. 3,

FIG. 5 shows an alternative method of undertaking compensation for awave movement for the lifting gear,

FIG. 6 shows still another alternative lifting and compensatingarrangement,

FIG. 7 shows in further detail a collapsible support structure,

FIG. 8 shows an alternative embodiment of the collapsible supportstructure shown in FIG. 7,

FIG. 9 illustrates the use of the method according to the invention forinstallation of a module from below and into an existing oil platform,

FIG. 10 illustrates use of the method for installation of a module to aplatform from a vessel on the exterior of the module frame, with the aidof a lifting frame,

FIG. 11 illustrates a construction method for oil platforms showing thefirst phase of the construction,

FIG. 12 shows the installation of the utility module that constitutesthe next phase of the construction,

FIG. 13 shows the utility module mounted and depending from theplatform's projecting beams,

FIG. 14 shows the platform after mounting is completed.

FIG. 15 shows a platform that is installed on a concrete base, and

FIG. 16 shows an application of the method for installation offoundation frames, manifold stations, satellites, etc.

The system consists of the following main elements as shown in FIG. 1:

The lifting gear 1 may consist of an ordinary crane, drum winch orlinear lifting mechanisms that obtain their power from a hydraulic powerpack 2.

From the lifting device 1 runs a suspending means 4 consisting of one ormore individual wires or lines passing through a gripping means having agripper mechanism 7, to a weight 10 that holds the suspending meanstaut. The gripper mechanism 7 is connected to the load 11, which mayconsist of a module, a deck, an equipment package or the like. Load 11is placed on a collapsible support structure 12 which stands on thevessel 13. Several forms of gripper mechanisms such as clamps or Jawsare conceivable, but mechanisms having self-inducing function areparticularly preferred: i.e., mechanisms that clamp harder and moresecurely the greater the load is.

The principle shown illustrates that by means of a special controldevice for the gripper mechanism 7, it will be possible to transfer theload to the suspending means while the load is at a standstill, i.e., atthe top of the wave movement.

The system includes a controlled press plate 6 which holds the grippermechanism 7 open until it is activated by remote control at a point intime determined by the speed and direction recording instrument 5.

On activation of the press plate 6 the gripper mechanism 7 is triggeredwith the aid of a spring 8. This causes means 4 to be locked againstupward movement relative to the gripper mechanism 7 so that load 11remains suspended by the means 4.

In the following are shown the main principles of the technical designof the equipment used for installation of modules directly from avessel.

FIG. 2 is a sectional view of the main components of the equipmentarranged for installation of a module. These consist of lifting gear 1,hydraulic power pack 2, controlled gripping means 14, cable weight 10,the supporting means being cables, positioning instrument 5, collapsiblesupport structure 12 and vessel 13.

The functional principles are as follows:

Mounted on or within the platform 3 is the lifting gear 1, for example,linear hoisting machines, drum winches or suitable hoisting equipment.From the lifting gear 1 are lowered, to within a few meters above sealevel, lifting cables 4 on which weights 10 have been mounted to holdthem taut, and so-called pilot cables 16, i.e., lightweight steel cablesor hawsers that the vessel crew can use for handling the weights.

The ship 13 has been fitted with a transport frame 20 having collapsiblesupport legs 12 for supporting the module 11.

In the lifting procedure, the ship 13 is positioned below the liftinggear 1 with the aid of the instrument package 18 that registers theposition and movement of the ship in relation to the platform. Thepositioning equipment may be of various types: mechanical with the aidof a so-called piano wire 17 suspending a weight 19 from the platform,by shortwave acoustic signals, light, lasers or by visual registration.

The vessel's movements are registered on the bridge, and are evaluatedin relation to the calculations forming the basis for the liftingoperation.

The operation starts with the use of the pilot cables 16 to guide theweights 10 and gripping means 14 into placement at the module's liftpoints. During this period the gripper mechanism 7 is not activated, andthe lifting cables 4 may pass freely through the gripper mechanism 7. Ifthe position and movement are within given parameters, the ship'scaptain will release the gripper mechanism 7 with the aid of, forexample, electrically controlled powder charges or hydraulic, pneumaticor manual triggers 15.

The mode of operation of the gripper mechanisms 7 is such that they canbe activated only while the load undergoes an upward movement. Also,after being activated, the gripper mechanism only permits the cable torun freely in the downward direction relative to gripper mechanism 7,which means that the cable is locked immediately on a directionalchange.

This principle enables the module to be lifted along the cable 4 of thevessel during the wave motion to the top of the wave. At the instant thevessel begins to move downward, module 11 will be suspended from thecable, and is lifted free of the support legs 12.

The support legs 12, which are collapsible, are activated and fold downrapidly so as to establish a distance between the vessel and the module.This is of major importance for preventing collision between the vesseland the load when the vessel is lifted by the next wave and, inaddition, floats higher in the water due to the removal of the load.

The vessel leaves its position, and the module may be hoisted up andsecured to the platform.

FIG. 3 shows the principle for one embodiment of a gripping means 14 inthe form of a gripper mechanism 7 with movable wedges, or keys.

There are several different ways to arrange the gripping means 14 andtrigger system. In FIG. 3 an alternative is illustrated where thegripping means is freely suspended on the cable system.

The gripper mechanism itself 7 is enclosed in a housing or harness 14',serving partly as a holder for the gripper keys, and partly as a simpleconnector for attachment to the load with the aid of, for example, aso-called bayonet coupling. Through harness 14 runs one or more liftingcables or wires 4 which at the upper end thereof are attached to thelifting gear, and at the lower end may be connected to a cable weight 10that holds the wires taut, and which overcomes the frictional forces inthe gripper keys and measuring/recording instrument 5.

The mode of function for the gripping means 14 is as follows:

In open position (deactivated state), the press plate 6 is pressed downand locked by a trigger 15. Press plate 6 in this position holds thegripper keys 7 open to allow the cables 4 to pass freely therethrough.

The recording instrument 5 has two functions:

a.) to register the vertical movement in the form of the speed anddirection of the load relative to the cable 4, and

b.) to activate a microswitch 22. This is done by the resistance torotation of the wheels of instrument 5 causing recording plate 21 to bepressed against a spring 23, which alternately turns the microswitch onand off depending on whether the movement is upward or downward.

This function may also be carried out electronically with theregistration of the upward/downward movement in the signals from therecording instrument 5.

Activation of the gripper mechanism can take place through thetransmission of an electrical signal from the bridge. The signal may besent regardless of whether the load is on the way up or down, sincemicroswitch 22 stops the signal from reaching the trigger mechanism 15until the load is moving upward relative to the cables. When the signalreaches the trigger mechanism 15, a powder charge is ignited, the safetycatch is released, and press plate 6 is lifted up by springs 8, whichsimultaneously push the gripper keys upward and into contact with cable4.

At the instant cable 4 begins to move upward relative to gripper keys 7,these are locked while undergoing a movement of 5-10 mm, whichcorresponds to the vertical movement for the load before the weight istransferred to the cable system. The wires will stretch slightly underthe load, with 30-50 mm found to be normal for module lifting. Thevertical speed attained by the load at this point in the movement isinsignificant.

In FIG. 4 an alternative arrangement of the press plate 6 and triggermechanism is illustrated. This arrangement increases the safety of therelease in that more than one activator 15', consisting of powdercharges, hydraulic pressure, etc., may be involved.

The system functions such that press plate 6 is provided with a groovein which are disposed a series of locking lugs 25 which in locked stateare pressed against a stopper ring 24. In the housing 14' for thegripper mechanism is disposed a piston 25 and one or more electricallycontrolled powder charges or solenoid valves connected to a hydraulicpressure source.

When the signal for release reaches the charge(s) or the solenoid valve,piston 25 is pressed upward, and it urges the locking lugs into thegroove in press plate 6. The latter is released and is pressed upward bythe force of springs 8. This causes the gripper keys to be pressedinward against cable 4, thereby locking it.

Rapid release of the load, i.e., on loading a module from a platformdown to a vessel, for example, is made possible by pressing the pressplate 6 downward and into locked position.

FIG. 5 shows an alternative method of undertaking compensation for thewave movement in the lifting system.

The lifting machine 1, which stands on a platform 3, is combined with ahydraulic accumulator 27 that allows the piston of the lifting machine,and with it the cables which are locked by the two upper gripper keys,to move in rhythm with the wave movement that the load imparts to thecables 4.

The recording instrument 5, together with the controlled gripper keys,are mounted in connection with the lifting machine 1 by means of thehousing, or harness 14'.

This system is also invertible, enabling the lifting machine to mounteddown by the module if this should be desired.

FIG. 6 shows an alternative lifting and compensation arrangementconsisting of two lifting machines 1 and 29 which operate in tandem. Themachines are placed atop one another, and cables 4 run through themboth. One of the machines may be used for lifting and lowering, forexample, while the other compensates for motion. This function may alsobe assigned to the upper machine 1. The machine responsible for wavecompensation 29 is equipped with a recording instrument 5 for motion anddirection as well as an ordinary actuator 30 for control of opening andclosing of the gripper mechanism in lifting and lowering operations.

The rapid lock mechanism, which is designed to stop the movement whenthe load is at its highest point in the wave, consists of a controlledvalve 28 that shuts off the flow of hydraulic oil from the liftingmachine 29 to the accumulator 27 when activated in accordance with theprinciples and equipment previously described.

The equipment illustrated in FIG. 6 may be mounted in inverted sequence,i.e., connected to the load instead of positioned up on the platform.

When the load is taken over by the cable system, the load will be liftedfrom the collapsible support structure shown in FIG. 7.

This illustration is one of several examples of how the collapsiblesupport structure may be arranged.

To the module 11 is fastened a release cable 33 which is connected viapulleys to a lock bolt 31 holding the structure locked in raisedposition. When module 11 is lifted, the release cable 33 pulls out lockbolt 31 and simultaneously assists in collapsing the structure's legs32, so that the brace 12 is laid down parallel with the structural frame20. When the module 11 is lifted from the ship, there is an alterationin both trim and displacement. This means the ship deck will now beresting higher in the water than in its loaded state. When the ship isagain lifted up by the waves, the collapsible support structure willprevent collision between the module and ship.

FIG. 8 shows an alternative method of arranging the support structure toavoid collision between load and vessel when unloading.

Cables 4 may be suspended at a slight angle, which on lifting willimpart to load 11 a small power component aftward or laterally relativeto vessel 13. The support structure 12 is arranged in such manner as tocreate a sufficient distance between the load and the vessel duringlifting. This is achieved most advantageously by dividing the structure12, as shown, so that one part moves with the load and will lie outsidethe vessel after lifting, while the part situated on the vessel ends upon the outside of the load when the load is hoisted up.

FIG. 9 shows that the principle may be used for installation of a modulefrom below and into an existing oil platform in accordance withNorwegian Patent No. 860856.

Module 11 arrives at support structure 12 by means of ship 13, and ispositioned below the platform module deck 3, on which lifting machines 1are installed on mobile frames and receive their power supply from theaggregates 2.

The module is hoisted as described earlier in FIGS. 2-4, and is movedhorizontally in and up onto module deck 3 where the module is secured tothe module deck 3 or is suspended therefrom.

FIG. 10 shows the invention used for installation of a module onto aplatform from a vessel, on the outside of the module frame or Jacket andthereupon, or up onto existing modules with the aid of a lifting frame.

Module 11 arrives with the vessel, is positioned under the lifting frame34 and lifted up by means of lifting machines placed on the liftingframe. With this method the module 11 is lifted through and up onto thelifting frame 24, and is then moved in onto the module deck.

The invention as described has given rise to a new design andconstruction method for oil platforms, as described in the following.

The costs connected with installation of oil platforms offshore or onland can be quite considerable, particularly due to the need to uselarge floating cranes. This is particularly true for platforms of asmaller size, where the cost of installation is especially high inrelation to the total construction cost of the platform.

Therefore, in the following we have chosen to present a design andconstruction method which can be fully executed without the use offloating cranes.

The platform may be built entirely as a framework of steel, theso-called "steel Jacket" platform, or with a substructure of concrete, aso-called "gravity base" platform.

We have chosen to show a design and construction method used for alightweight wellhead platform of steel in FIGS. 11-14, and as a wellheadplatform in concrete in FIG. 15.

FIG. 11 illustrates the first phase of construction.

The platform's frame or jacket 36 is built with projecting support beamsor skids 35 mounted on the top or somewhat further down on the Jacket orframe. Normally it will also be possible to install a crane and flaretower prior to the installation of the jacket on the oil field.

Jacket 36 is installed on the field by launching directly from barges,and it is held and positioned with the aid of floats fastened to thejacket. Launching the jacket and securing it to the sea bed, so-calledpiling, can be done by drawing the Jacket down toward thebottom--preferably over pre-drilled wells--with the aid of the liftingmachines, and steering it into position on piles sunk in the sea bed.

The modules and deck intended for the platform arrive on supply ships orbarges for installation as follows:

The platform's own diesel motor driven cranes hoist the lifting gear 1into place with cables 4. The vessel 13 preferably arrives first withthe living quarters module 37 or the helicopter deck, which is lifted upby means of the method described earlier. The module may be lifted upthrough the frame system and positioned thereon, or it may be mounted tobe freely suspended from the support beam 35. This is a matter ofchoice.

The advantage of installing the helicopter deck and living quartersmodule first is obvious, for the installation crew can live on theplatform and be transported by helicopter from the mounted helicopterdeck.

FIG. 12 shows the installation of the utility module 38, which ishoisted into place with the aid of lifting machines 1 and cables 4, aspreviously described. Note that the utility module in this case is atop-suspended or depending module. This is a new method by which tomount modules, affording a reduction in the steel weight of the module,as well as facilitating its replacement or dismounting in the case ofconversion or removal of the entire platform.

FIG. 13 shows the utility module 98 mounted on and depending from theplatform's projecting beams. From this position it may later bereplaced/removed by reversal of the lifting process.

The equipment deck 29 with a wellhead Christmas tree, pipe systems, etc.installed thereon is mounted directly from a vessel as shown, and ismoved horizontally into place within the platform if desired.

FIG. 14 shows the platform fully mounted. The living quarters module 37,with the helicopter deck, is mounted highest and atop the liftingframes. The utility module 38 is mounted for top-suspension below theliving quarters module.

The equipment deck 39 with its intermediate deck and equipment ismounted within and between the platform frame system, and the weatherdeck 40--which may serve as a storage area for drill pipes, etc.--ismounted between the platform's lifting frames. On the lifting frames itis possible for the drilling and well maintenance equipment 42 to bemoved. The flare tower 41 can be mounted to best advantage on theoutside of the frame system, enabling the frames or skids to be usedfreely for lifting gear or drilling rigs 42.

As is apparent from the illustration, the platform design andconstruction method is very flexible with respect to mounting andreplacement of modules, decks, equipment, etc., by means of the framesystem and the described lifting principle.

FIG. 15 shows the wellhead platform described above designed with aconcrete base.

It is important to emphasize that the platform may be built with a beamsystem of steel or concrete according to choice, and that the modulesmay be designed as suspended modules or standing modules as desired.

The platform may be mounted on the field, for example, as merely aconcrete structure that is floated out onto the field without modules.

This results in better stability and lower buoyancy requirements thanfor platforms having modules mounted thereon. Here there is animplication of considerable cost savings, particularly for platforms foruse at great sea depths.

This platform is very simple to mount: the modules are positioned on theoutside of the concrete shaft and are thus situated very securely withrespect to possible blowouts or fires in the processing plant. Theplatform is constructed with suspending or dependent modules, making itpossible for the modules to be replaced or removed easily andfacilitating the disassembly or, if necessary, the moving of theplatform. The suspended modules have a lower steel weight than standingmodules, and may be constructed and mounted considerably moreinexpensively by means of the described method.

FIG. 16 shows an application of the method for installation offoundation frames, manifold stations, satellites, etc., by means ofdrilling rigs, tension leg platforms, or the like. The method consistsof transferring the equipment to a drilling rig or platform inaccordance with the invention, instead of using crane vessels to set theequipment on the sea bed. Thereafter the installation onto the sea bedfrom the platform is carried out either by means of the lifting gearassociated with the drilling rig, or with the aid of the hydrauliclifting machines previously described.

I claim:
 1. Apparatus for transferring a load movable in a substantiallyvertical direction to a temporarily stationary suspending means at aninstant when the load has no significant kinetic energy, the apparatuscomprising at least one gripping means, a recording or sensing devicewhich registers when the movement of the load reverses at said instant,said sensing device, after a prior command, emitting a signal thatcontrollably activates the gripping means for locking the load to thesuspending means at the same instant, the gripping means including ahousing which encloses the suspending means, said gripping means furthercomprising a gripper mechanism including keys which are held at astarting position in spaced relationship to the suspending means, whilenearly enclosing the suspending means, and which on activation releasesa press plate enabling the keys to lock the load to the suspending meanson a specific direction of movement of the load or the suspending means.2. Apparatus for attaching a load which cyclically moves up and down toa stationary cable suspended from an installation, the apparatuscomprising a housing adapted to be attached to the load; a grippingmember mounted to the housing and movable between a first position inwhich the gripping member permits relative movement between the cableand the housing and a second position in which the gripping memberprevents relative movement between the cable and the housing and therebylocks the housing to the cable; a sensor for determining relativemovement between the cable and the housing and a directionality of therelative movement; and triggering means operatively coupled with thesensor and the gripping member for moving the gripping member from itsfirst position to its second position in response to a reversal of thedirectionality of the relative movement between the housing and thecable to thereby secure the housing, and therewith the load suspendedtherefrom, to the cable for subsequent lifting of the load with thecable.
 3. Apparatus according to claim 2 wherein the load is carried ona vessel subjected to up and down motions induced by waves, and whereinthe triggering means is moved into the second position in response to asignal from the sensor indicating a reversal of the relative movementbetween the housing and the cable from an upward direction to a downwarddirection so that the load becomes suspended from the cable when thevessel is on a crest of a wave.
 4. Apparatus according to claim 2including means for maintaining the cable taut.
 5. Apparatus accordingto claim 2 wherein the sensor includes means engaging the cable forsensing relative movement between the cable and the housing. 6.Apparatus according to claim 2 including a hoist mounted on theinstallation and operatively coupled with the sensor, the hoist liftingthe cable upwardly upon activation of the triggering means to move thegripping member to its second position.
 7. Apparatus according to claim2 including a hoist for lifting and lowering the cable, and a hydraulicaccumulator operatively coupled with the hoist for compensating relativemovement of the load with respect to the installation.
 8. Apparatusaccording to claim 7 wherein the hoist is mounted on the installation.9. Apparatus according to claim 7 wherein the hoist is mounted on theload.
 10. A method of safely lifting a load carried on a vesselsubjected to typical vertical up and down motions of the vessel as aresult of waves, the method comprising the steps of suspending a cablefrom a stationary hoist located generally above the vessel; attaching agripping mechanism disposed about the cable to the load so that thegripping mechanism can move along the cable as the vessel and therewiththe load moves up and down relative to the cable; operatively coupling asensor to the gripping mechanism and the cable; when it is desired tocommence lifting the load off the vessel, activating the sensor to senserelative movements between the cable and the gripping mechanism;energizing the gripping mechanism to permit the gripping mechanism tomove relative to the cable in an upward direction and, upon a reversalof the direction of relative movement between the gripping mechanism andthe cable from an upward direction to a downward direction, to securethe gripping mechanism to the cable and thereby suspend the load fromthe cable by preventing further relative movement of the grippingmechanism along the cable in said downward direction; and activating thehoist to lift the cable and therewith the gripping mechanism and theload upwardly away from the vessel.
 11. A method of transferring a loadfrom a vessel which is cyclically moved in opposite vertical directionsby waves to an installation comprising the steps of suspending asuspension member from a hoist mounted on the installation; maintainingthe suspension member taut; attaching a gripping mechanism to the loadand extending the suspension member past the gripping mechanism so thatthe gripping mechanism can move up and down relative to the suspensionmember; sensing relative motion between the suspension member and thegripping mechanism resulting from relative vertical movement between thevessel and the installation; engaging the gripping mechanism and thesuspension member to prevent further relative movement between them in avertical direction in response to sensing a reversal of the relativemotion between the gripping device and the suspension member so that thegripping device secures the load to the suspension member; andthereafter activating the hoist to lift the suspension member andtherewith the load away from the vessel.
 12. A method according to claim11 wherein the step of suspending comprises suspending a cable from thehoist.
 13. A method according to claim 11 including the steps ofproviding a support between the vessel and the load which positions theload a predetermined distance above a support surface of the vessel, andreducing a height of the support when the load becomes suspended fromthe suspension member.
 14. A method according to claim 13 wherein thestep of reducing the height comprises the step of collapsing thesupport.